Digester



June 2, 1964 J. R. sTARRr-:TT

DIGESTER Filed Nov. 50, 1959 BY 3mm? W.

United States Patent O assigner to The Springfield, Ohio, a corporation This invention relates to continuous treatment digesters, as used for example in the reduction of wood chips to produce paper pulp, the invention having special reference to digesters using a moving conveyer system to conduct fibrous material to and from contact with the chemical liquors and vapors which attack the material in a manner to free individual fibers for separation.

The object of the invention is to simplify the construction as well as the means and mode of operation of digesters, whereby such digesters may not only be economically manufactured, but will be more efficient and satisfactory in use, adaptable to a wide variety of applications, and be unlikely to get out of order.

An objective in the design of continuous treatment digesters of the moving conveyer type is to achieve a thorough and effective impregnation and treatment of the llbrous material with a minimum of physical disintegration and it is a specic object of this invention to achieve this result to a larger extent than has heretofore been known.

Another object of the invention is to introduce a new mode of mounting and guiding the continuous conveyer means enabling a reduction in the length of required guide rail.

A further object of the invention is to provide ilights on the continuous conveyer means having a configuration adapted to avoid changes of substantial extent in the spacing between portions of adjacent flights as the conveyer means enters upon and completes a turning movement.

Still another object of the invention is to achieve a containment of substantially constant volume between the flights of the conveyer means despite turns therein.

A still further object of the invention is to obviate binding and the creation of excessive frictional forces at the turns of the conveyer means.

A further object of the invention is to provide a digester possessing the advantageous structural features, the inherent meritorious characteristics and the mode of operation herein mentioned.

With the above and other incidental objects in view as will more fully appear in the specification, the invention intended to be protected by Letters Patent consists of the features of construction, the parts and combinations thereof, and the mode of operation as hereinafter described or illustrated in the accompanying drawings, or their equivalents.

Referring to the accompanying drawing wherein is shown one but obviously not necessarily the only form of embodiment of the invention,

FIG. 1 is a view in longitudinal section of a continuous treatment digester in accordance with the illustrated embodiment of the invention;

FIG. 2 is a view in cross-section taken substantially along the line 2-2 of FIG. l; and

FIG. 3 is a fragmentary view of the lower end of the digester, as seen in FIG. 1, and enlarged with respect to FIG. 1.

Like parts are indicated by similar characters of reference throughout the several views.

Referring to the drawing, a continuous digester in accordance with the illustrated embodiment of the Vinvention comprises essentially a vessel holding a quantity of a cooking liquor or vapor or both, with continuous conveyer means operating to conduct the fibrous material ice to and through the cooking liquors and vapors. The illustrative form of the invention contemplates a vessel in the form of a cylindrical tube shell used, as shown, in an inclining attitude with the tube shell being suitably supported as on pads 11. Upper and lower ends of the tube shell 10 are closed by respective caps 12 and 13. A closure unit 14 is received in the lower end of the tube shell and constitutes a false bottom, being interposed between the cap 13 and the interior proper of the tube shell. The unit 14 comprises a cylindrical portion 15 slidably mounted in the shell 1i), and, rigidly secured thereto, a hemispherical part 16 coaxial with the tube shell 10 and having its concave surface facing inwardly toward the shell interior. The radius on which the part 16 is formed corresponds to or is equal to that on which the tube shell 16 is formed.

The cylindrical part 15 extends inwardly of the tube shell beyond the inner end of the hemispherical part 16 and provides rotary bearings for a transverse shaft 17 on which is one or a pair of rotary discs 1S providing a guide and mounting for a continuous conveyer chain or chains 19, it being understood that the conveyer means comprises one or a plurality of chains and guides therefor as may be required by the size of the installation and the character of the work to be done. There is in the illustrated instance, as indicated in FIG. 2, two parallel chains 19 and there are accordingly two rotary discs 18 mounted in transversely spaced apart relation on the shaft 17 to be aligned with and engaged by respective chains 19. The chains 19 further encompass and have a driven engagement with sprocket wheels 21 at the opposite or upper end of the tube shell, the arrangement being one to provide long parallel reaches of chains throughout the major length of the tube shell. The sprockets 21 are secured to a transverse shaft 22 suitably rotated from outside the digester. Extending longitudinally of the tube shell 10 between the rotary discs 18 and sprockets 21 is a central partition 23 which in the illustrated instance is made hollow for a zoned movement of cooking liquors in a manner which is unnecessary here to consider. Insofar as the present invention is concerned the partition 23 serves merely as a longitudinal medial division means separating the interior of the tube shell 10 into an upper flight passage 24 and a lower llight passage 25, these being interconnected at their ends.

Common to the pair of conveyer chains 19 and longitudinally spaced apart thereon are flights 26 which occupy approximately transverse positions in the tube shell and till or substantially ll the semi-circular space between the partition 23 and the wall of the tube shell in each ilight passage. Thus, and as shown in FIG. 2, each llight 26 has a shape corresponding approximately to the interior cross-section of the tube shell 10 above and below the partition 23. Slots 27 and 28 extend from the lower edge of the flight and receive the chains 19 which are welded or otherwise secured to the flights at the bottom of such slots. Mounted on the upper surface of the partition 23 in a manner to project upwardly into v the flight passage 24 is a longitudinally extending pair of guide rails 28 on which the chains 19 are mounted and which align the conveyer means in the upper flight passage. Within flight passage 25 the conveyer means is in a dependent position and guide means like the rails 28 are unnecessary although partial guide means leading the conveyer into the passage 25 may be provided as hereinafter shown.

The flights 26 have the function of paddles or impellers in the tube shell 10 and may be considered to have upwardly and downwardly projecting portions with respect to the chain 19 upon which they are mounted. The upwardly projecting portion assumes a position normal to the chain link to which it is secured. At about the point of attachment of the flight to the chain link, however, the flight is bent so that the downwardly extending portion is inclined relative to the upwardly extending portion, the direction of inclination being forwardly or in the direction of travel of the conveyer chains as indicated by the arrow in FIG. 1. As a result of this configuration of the flight, the downwardly extending portion leads the flight into the 180 turns at the ends of the conveyer chains in a manner to minimize variations in spacing between adjacent flights as the successive flights enter the turns at the upper and lower ends of the tube shell.

The inclined attitude of the tube shell is used to obtain a gravity feed of fibrous material to the tube shell as well as from it. On what may be considered the upper side of the shell is an inlet opening 29 connected by fitting 31 to a valve housing 32 in which is a rotary valve 33. Fibrous material is admitted to the housing 32 through an inlet opening 34 and is carried by rotation of the valve 33 in predetermined metered quantities to the fitting 31 and inlet 29, the construction and arrangement of the valve being such as to preclude an escape of vapors under pressure as might be contained in the tube shell 1t). Entering the upper flight passage 24 of the tube shell the fibrous material is picked up by successive flights 26 and moved downwardly in the shell toward the hemispherical part 16 which, in conjunction with the shaft 17 and lower end of partition 23, defines an arcuate passage 35 in which the material moves through a 180 turn into the lower flight passage Z5. There the material continues to be propelled by the flights 26, moving upwardly in the tube shell until it encounters an outlet opening 36 therein. Dropping through the opening 36 and through a fitting 37 mounted thereon the material is carried off by a rotary valve 325 like the valve 33 and operating with similar effect although in this instance to carry out a controlled discharge of treated material rather than an admission of fibrous material for treatment. In connection with such treatment it will be understood that the tube shell lll contains a quantity of a cooking liquor and that its interior may or may not be under fluid pressure. The liquid level lies beneath the inlet 29 and outlet 36 so that the fibrous material in moving as described from the tube shell inlet to the tube shell outlet is conducted into, through and out of the bath of chemical liquors. The liquors are supplied in a suitable manner through an inlet not shown and may be drained through a valve controlled outlet fitting 39 in the bottom end cap 13. Also, suitable means may be provided to heat the contained liquid, as through external steam coils.

The instant conveying apparatus is unique in its adaptability to a turning of the conveyed material through a 180 angle without any such appreciable loss of volume between adjacent flights as would increase frictional resistance, creating obstructions and abnormal strains. This unique concept of conveyer operation is at least in part due to the angular configuration of the flights 2-5. The forwardly bent portion of each flight leads the upper portion, which is normal to the chain links to which it mounts, by a certain predetermined distance. Were the motion of the flights to be examined by taking cutting planes parallel to the partition 23 it would be seen that the lower edge of the flight is well into the turn within arcuate passage 35 before its forward motion is appreciably decreased relatively to the corresponding portion of the next following flight. Also, the relationship of the lower' edge of the flight to the partition 23 is substantially constant thus preventing the flight from moving away from the partition and making possible obstruction and binding as the flight attempts to restore itself to an original attitude. The fibrous material enters the tube shell 10 at a predetermined rate, in relation to the movement of the conveyor means, so that the spaces between the flights are CJI loosely packed with the material as the flights approach and enter into the arcuate passage 35. Were the flights to be straight, that is with the lower portion parallel to the upper portion, cutting planes taken as before would reveal that the only plane of a flight traveling at a constant rate of movement through the turn is that plane taken through the center of the conveyer chain. All planes taken through the flight above the chain progressively increase in their rate of movement as the cutting plane appreaches the maximum distance from the chain. Correspondingly all planes taken through the flight below the conveyor chain progressively decrease in rate of movement. Also the lower edge of the turning flight moves vertically away from the partition creating an obstruction to material flow. If the flight entering the turn or arcuate passage 35 is decreasing in rate of motion in its lower section, while the trailing or next following flight is traveling in a straight line or at a constant rate it will be apparent that the volume occupied by the loosely packed fibrous material will be decreased below the center line of the chain and will be increased above the center line. Further the lower edge of the flight, moving at a lower velocity and being raised a substantial distance from the partition, will restrict movement of the fibrous material into the passage 35. An abrupt decrease in rate of movement will create a decrease in volume between the flight entering passage 35 and the next following or trailing flight, with the result that the conveyed material is compressed, setting up frictional resistance and abnormal strains as described.

According to a further feature of the invention portions of the upper and lower flight passages 24 and 25 have been blocked off through the use of inserts 41 with the view of further compensating for decreasing velocities and volumes below the center of gravity of the conveyer chain. The flights 26 are formed to conform to this shape of the flight passages, being in this and other respects made slightly smaller in size than the available space of the passages to allow for operating clearance.

Also entering into the successful conveying of the material around the turn at the bottom of the digester is the design of the hemispherical part 16, the conveyor chain size and the flight spacing. The movement of the flights through the acuate passage 35 is indicated in dotted outline in FIGS. 1 and 3 wherein the various positions assumed by the individual flights as they move through such passage are illustrated. The force applied to the flights to create motion, or the conveyor chain in this case, should be applied at or very near the center of gravity of the flight to create an even load. The flight spacing should not exceed that distance necessary to create a contained volume equal to that of the hemispherical part creating the turn. If the contained volume between flights is greater, the amount of force necessary to execute the turn will be greatly increased, because the flight must exert a force opposite in direction to its travel. If the contained volume between flights is less than that of the turn more flights are required which increase the cost, and, since the additional flights are of little or no assistance, they become impractical. The volume of the hemispherical part is determined by its radius which, as noted, equals the radius of the tube.

The closure unit 14 has a rod 42 attached thereto which extends through a stufiing box 43 on the bottom of the closure cap 13, projecting through and beyond such fitting. Surrounding the projecting end of the rod is amcompression spring 44 based on a plate 45 connected to and forming a part of the fitting 43 and contacting at its other end a stop 46 limiting against a nut 47 adjustably mounted on the outer end of the rod 42. The arrangement is one to apply a resilient outward pressure upon the closure unit 14 in a manner to maintain through the rotary discs 18 a tension upon the chains 19. Also connected to and forming an integral part of the closure unit 14 is a tongue 48 telescopieally engaging the lower end of the partition 23. Secured to the tongue 48 on the upper edge thereof are fragmentary chain guides 49 acting as continuations of the guides 28 and leading the chain onto the rotary discs 18. Secured to the lower edge of the tongue 48 is a further guide 51 which assists in maintaining proper alignment of closure 14 within shell 10.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particularly features of advantage before enumerated as desirable, but which obviously is susceptible of modiiication in its form, proportions, detail construction and ararngement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise but one of several modes of putting the invention into effect, and the invention is therefore claimed in any of its forms or modfications within the legitimate and valid scope of the appended claims.

Having thus described my invention, I claim:

l. A continuous treatment digester of the moving conveyer type, including a tube, closures for the ends of said tube including a closure unit at one end thereof having an inwardly directed hemispherical surface, a central partition in said tube disposed transversely thereof, having its respective ends short of said end closures and said hemispherical surface, said partition thereby deiining longitudinally extending flow passages in said tube to either side thereof connected to its respective ends, means on said closure unit forming an extension of said partition and defining an arcuate passage connecting said flow passages adjacent said hemispherical surface, continuous flexible conveyer means extending longitudinally over said partition and through said arcuate passage, longitudinally spaced apart iiights on said conveyer means each having portions on opposite sides of said conveyer means, the outermost portions of said iiights being generally normal to said conveyer means to either side of said partition and the innermost portions thereof being inclined relative thereto in the direction of their movement, said flights being carried thereby in one direction through one of the longitudinally extending ow passages and moving through said arcuate passage to be carried in reverse direction through the other longitudinally extending tiow passage, inlet and outlet openings in said tube, fragmentary material being received through said inlet and carried by said conveyer means in a loosely packed form between adjacent tlights, the disposition of the innermost portions of said ights relative the outermost portions thereof being such to maintain a substantially uniform volume and positive flow of the material between adjajacent flights in entering and passing through said arcuate passage to said outlet opening.

2. A continuous treatment digester of the moving conveyer type, including a tube, closures for the ends of said i tube including a closure unit at one end thereof having an inwardly facing hemispherical surface, a longitudinally extending centrally disposed partition in said tube terminating at its one end short of contact with said hemisphercial surface, said partition defining longitudinally extending flow passages in said tube to opposite sides thereof connected at one end through an arcuate passage defined by said closure unit including said hemispherical surface, continuous flexible conveyer means extending longitudinaly over said partition and around said one end thereof, means on said closure unit forming an extension of said partition and guiding said conveyer means around said one end of said partition through said arcuate passage, longitudinaly spaced apart flights on said conveyer means each connected approximately at its center of gravity to said conveyer means and respectively including outer portions generally normal to said conveyer means and portions extending inwardly of the conveyer means in the direction of said partition, said inwardly extending portions of said flights being inclined in the direction of travel of said conveyer means, said iiights being thereby formed to maintain a continuous substantially uniform free iiow movement of material through said passages including said arcuate passage and maintain a substantialy uniform volume of the material.

face, said surface being formed on a radius at least as large as the radius on which said tube is formed, means defining an inlet to and an outlet from said tube, conveying means in said tube for continuously conducting fragmentary material introduced through said inlet lengthwise of the tube and to said one end thereof, iiights on said conveyer means for receiving the fragmentary material therebetween in a loosely packed condition formed to maintain the volume of the material therebetween and turn the material in said tube on said hemispherical surface to reverse the direction thereof to the means defining said outlet, said flights being bent in an area adjacent their midpoints to incline at least their innermost portions in the direction of their travel and relative their outermost portions to thereby adapt them to reduce fric-l tion and prevent binding in turning the material on said hemispherical surface.

4. A continuous treatment digester of the moving conveyer type, including a cylindrical tube having inlet and outlet openings on opposite sides thereof, closures for the ends of said tube including a closure unit at one end thereof mounted in sliding engagement therewith and having an inwardly facing hemispherical surface formed on a radius substantially as large as the radius on which said tube is formed, partition means in said tube arranged to place said inlet and outlet openings to opposite sides thereof and terminating at one end short of contact with said hemispherical surface to form therewith an arcuate passage connecting the spaces defined in said tube to opposite sides of said partition means, continuous liexible conveyer means extending longitudinally over said partition means and around said one end thereof, means on said closure unit engaging and tensioning said conveyer means, and longitudinally spaced apart flights on said conveyer means including portions projected inwardly thereof inclined in the direction of their movement and relative their outer portions adapting said flights to maintain a substantially uniform volume therebetween in moving through said arcuate passage.

5. A continuous treatment digester of the moving conveyer type, including a tube having a central partition defining spaced passages extending longitudinally thereof, closures for the ends of said tube including a closure unit at one end thereof mounting rotary conveyer guide means forming an extension of said partition and providing an arcuate passage connecting said spaced passages, continuous conveyer means in said tube passing over said rotary guide means, means for driving said conveyer means and longitudinally spaced iiights on said conveyer means having relatively inclined outer and inner portions, the portions inwardly thereof being uniformly inclined relative the outer portions and in the direction of movement of said conveyer means.

6. A continuous treatment digester of the moving conveyer type, including a tube adapted to be supported in an inclined position, a partition in said tube dividing the interior thereof into upper and lower iiight passages, said partition terminating at its lowermost end short of the bottom end of said tube, a guide rail on said partition extending upward in said upper ight passage, a continuous conveyer chain extending longitudinally through said upper and lower Hight passages and around the lower end of said partition, said chain being supported on said rail in elevated relation to said partition in said upper ight passage, means for driving said chain, spaced apart iiights on said chain, each having relatively bent portions projecting inwardly of said chain arranged to lead the ilights around the lower end of said partition whereby to maintain substantially uniform volume between adjacent flights as they move around the lower end of said partition.

7. A continuous treatment digester of the moving conveyer type including a tube adapted to be supported in an inclined position, partition means in said tube dividing it into upper and lower iiight passages, said partition means terminating at its lowermost end short of the bottom end of said tube, a closure unit slidably mounted in the bottom end of said tube providing an inwardly facing hemispherical surface adjacent and spaced from the lower end of said partition means, guide means on said partition means, continuous conveyer means extending longitudinally through said upper and lower ight passages and supported on said guide means, said closure unit having guide means forming an extension of said partition means at its lower end and rotary guide means for said conveyer means thereon, spaced apart flights on said conveyer means each having portions projecting outwardly of said conveyer means substantially normal thereto and portions projecting inwardly of said conveyer means and inclined in the direction of its travel, means for introducing fragmentary material to said conveyer means in the upper flight passage and means deining an outlet for such material from the lower ight passage, said partition means and extension thereof on said closure unit defining an arcuate passage with said hemispherical surface connecting said upper and lower flight passages whereby to direct material continuously through said upper flight passage and through said arcuate passage to said outlet without interruption.

References Cited in the file of this patent UNITED STATES PATENTS 2,235,856 Waechter Mar. 25, 194l 2,235,992 Hapman Mar. 25, 1941 2,335,611 Pray Nov. 30, 1943 2,488,671 Lehman Nov. 22, 1949 2,966,215 Durkee Dec. 27, 1960 

3. A CONTINUOUS TREATMENT DIGESTER OF THE MOVING CONVEYER TYPE, INCLUDING A GENERALLY CYLINDRICAL TUBE, CLOSURES FOR THE ENDS OF SAID TUBE INCLUDING A CLOSURE UNIT AT ONE END THEREOF HAVING AN INWARDLY FACING HEMISPHERICAL SURFACE, SAID SURFACE BEING FORMED ON A RADIUS OF AT LEAST AS LARGE AS THE RADIUS ON WHICH SAID TUBE IS FORMED, MEANS DEFINING AN INLET TO AND AN OUTLET FROM SAID TUBE, CONVEYING MEANS IN SAID TUBE FOR CONTINUOUSLY CONDUCTING FRAGMENTARY MATERIAL INTRODUCED THROUGH SAID INLET LENGTHWISE OF THE TUBE AND TO SAID ONE END THEREOF, FLIGHTS ON SAID CONVEYER MEANS FOR RECEIVING THE FRAGMENTARY MATERIAL THEREBETWEEN IN A LOOSELY PACKEDCONDITION FORMED 